Visit the power supply section of any reputable online retailer and the choice of quality ATX PSU's is often plentiful. However, if you've ever tried to build a MicroATX or FlexATX system such as a Home Theatre PC or Shuttle system you will have undoubtedly realised that the choice of PSU's is much more limited. In fact, I'd be willing to place a wager that most of you will have swallowed your pride, tried to forget all the stories about what a poor quality PSU can do to your PC and proceeded to build your new system with whatever generic heap of junk came bundled inside the case. Bad idea.

As I've been pushing on OC3D for ages, choosing a decent quality PSU for your PC system whatever its size or application is crucial. Not only are you putting your hardware at risk by choosing an inferior PSU, but if you value silence and want to save a few quid on your electricity bill a quality PSU is an absolute must. One such PSU manufacturer that comes highly recommended from Overclock3D is be quiet!Snugly tucked under the umbrella of parent company Listan, be quiet! made their first big appearance in the UK back in 2008 with a solid 650W ATX PSU from their Dark Power Pro range.

Today however, I'm going to be taking a look at be quiet's first ever SFX (Small Form Factor) PSU. Measuring in at 125x100x63.5mm (WxHxD) with a 350w output, can this diminuitively sized PSU provide small factor PC builders with a decent alternative to the low quality SFX PSU's pre-installed in their system chassis? Let's see what be quiet have to say...

SFX POWER is an ultra-efficient power supply unit that reliably supplies your PC with power and energy in the same way as a human heart supplies the body with energy. Compact and with the latest use of technology SFX POWER meets the demands of a premium product and of course with the customary be quiet! quality low noise levels. SFX POWER are powerful hearts from be quiet! for compact PC systems. Our SFX POWER power supply units provide your PC with maximum power. But you don’t have to compromise on brand, quality or security. In addition to that you are helping the environment, because in developing the SFX POWER we place great value on the efficient use of energy. The result: A high level of energy efficiency of up to 86%.

With a finger on the pulse of technology. Latest SFX 12V Version 3.2 80mm quality fan Dual Rail (2 separated 12V rails) Hold-up time of >17ms (at 100% Last) Active PFC with a PF of 0.99 >0,9 (at 100% load) Long service life of up to 100,000 hours at 25° Celsius

With features such as 86% efficiency, dual +12v rails and sleeved cables its easy to forget that we're not looking at the specs of a full fat ATX PSU here. Even when moving on the rail layout chart, the 20/22A distribution on the +3.3v and +5v rails along with 14/16A on the +12v1 and +12v2 rails is very much what would be expected of a 350w ATX unit. Of course, the proof of the SFX Power's capabilities will be in the testing, so lets swiftly move on to the packaging and appearance of the PSU over the next page before we get down to business.

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Packaging & Appearance

In much the same style as be quiet's other PSU's, the SFX Power is presented in a plain black box accompanied with a grey gradient stripe down the right-hand side. The size of the box is obviously quite small and can roughly be compared to the dimensions of a Cornflakes box, albeit at almost half the height. Very little information is printed on the front of the box, with be quiet saving diagrams of the PSU's form factor, cables and rail distribution charts for the back.

Packaging is a bit on the sparse side with the unit receiving only a bubblewrap bag to protect it from rough hands of a courier. However the saving grace here is the unit is quite light and therefore doesn't inflict damage to its self under the force of its own weight. Other contents include a power cord, some cable ties, case screws and a manual. Basically everything needed to get you up and running.

Being the first Small Form Factor PSU I've seen in the flesh, it really is amazing just how small the unit is. Even the fairly standard sized OCZ PSU (pictured above right) towers over the be quiet. The use of an 80mm fan does raise a few concerns in my head about just how quiet the unit will be when running at full load, especially when it looks like be quiet! could have probably squeezed in a 92mm fan to achieve a slightly more favourable CFM-Noise ratio. Obviously we'll find out soon enough.

Unlike the shiny electroplated finish of the Dark Power Pro range, the SFX Power is presented in a plain matte black powdercoat. This is probably a good thing as I don't imagine that anyone looking to purchase a new PSU for their MicroATX PC would be remotely interested in its appearance. Never less, be quiet! have still added a small personal touch to the side of the unit by imprinting their own logo.

At the top of the unit is the obligatory specifications stickers which is mostly taken up by the rail output chart we saw back on the previous page. The front of the unit has the usual honeycomb meshed grill used on almost all modern ATX PSU's whereas the back is fairly void of anything other than a couple of barcode stickers and a small vented area above the cable outlet.

Now let's move to the next page where we check out what cables are included and the innards of the unit.

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Cables, Connectors & Internal Components

While the normal rule for an ATX PSU is more connectors = better, builders of small form factor PC's will undoubtedly be wanting just the right amount of cables required to do the job. After all, with SFF PC's being...well small, space is at a premium and having a big bundle of unused cables will only hinder airflow. At first glance, the SFX Power 350w does seem to have a fairly balanced number of connectors, but let's pull off the elastic band and find out for sure!

be quiet! SFX Power 350w Connectors

ATX Connector

Native

20+4 Pin

EPS-12v / P4-12v Connector(s)

Native

1x 4 Pin

Molex Connectors

Native

3x

Floppy Disk Connectors

Native

1x

SATA Connectors

Native

2x

PCI-E Connectors

Native

1x 6 Pin

With 3x Molex and 2x SATA connectors, the SFX Power should suit most peoples needs for a basic system setup. However, since the cost of high capcity storage has plummeted over the past year there has been a growing trend for people to use small form factor PC's as cheap NAS boxes. For this reason alone I dont think it would have hurt too much for be quiet to bump up the number of SATA connectors to around 4. Just in case.

Everything else is pretty much as you'd expect. You get a 20-Pin ATX connector that can be bumped up to the newer 24-Pin version by means of attaching a small connector block, a single 4-Pin P4-12v motherboard connector and a 6-Pin PCI-E connector. As far as I'm aware, there aren't any graphics cards out on the market at the moment which require a single 8-Pin PCI-E connector, so providing you're not intending on cramming a GTX285 inside your SFF PC, this should be perfectly adequate.

Moving on to the internals, it goes without saying that everything is tightly packed. Interestingly though, the SFX Power does not have any heatsinks strapped to its mosfets and instead uses only thin pieces of metal much like heatspreaders to dissipate the heat. This is most likely due to the low profile height of the unit making it near impossible to install any kind of finned heatsink without blocking airflow from the fan.

A small amount of EMI filtering is provided on the the mains inlet with the live/neutral wires being wrapped around a ferrite choke. This may not be quite as effective as the full EMI/RF filtering circuits used on some PSU's, but should still help to keep any internally generated noise from the MOSFET's and other components contained within the device, while also preventing external AC line noise from entering the PSU.

Going in for a close look at the main capacitor over on the primary (high-voltage) side of the unit, the small little logo printed just to the side of the white stripe in the picture above-right tell us that this is a Japanese part manufactured by Hitachi. Furthermore the 105°c specification also indicates that be quiet! haven't cheaped out on components for this PSU either.

Finally, the only part of the whole unit that gets me worried is the 80mm fan. Not only is it an 80mm fan, but it is also a 12mm deep version which means that there really isn't much room to optimise the blades for maximum airflow at low speeds. Unfortunately searching for the model number (MGA8012ZR) on the web turned up no results, nor did looking at Protecnic Electric's abysmal website. So we'll just have to wait and see how this performs over on the next page...

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Simulated Load Testing

To provide accurate and consistent results in all of our PSU testing, Overclock3D uses professional grade DC electronic load equipment capable of placing a sustained load of 3690w across a total of six rails (including +5vsb and -12v) on the PSU! This is achieved by using a combination of SunMoon and Analogic electronic load equipment which allow us to adjust amperage loads in increments as small as 0.01A while also measuring voltage and wattage readings on-screen.

During today's tests, we will be placing the be quiet 350w SFX PSU under 25%, 50%, 75% and 100% load levels at room temperature. Unfortunately, due to the size of the PSU on test today no 50°C 'hot-box' testing could be performed.

be quiet! 350w SFX Results @ Room Temperature

+3.3v

+5.0v

+12v

+5vSB

-12v

AC Watts / DC Watts

Efficiency

Intake / Exhaust

Δ Temp

T1 (Low)

3.75A

4.00A

4.25A

0.62A

0.12A

105w / 88w

83.80%

27.2°C / 44.2°C

17.0°C

3.37v

5.09v

11.92v

5.14v

-11.90v

T2 (Med)

7.50A

8.00A

8.50A

1.25A

0.25A

205w / 176w

85.85%

27.0°C / 45.0°C

18.0C

3.35v

5.03v

11.94v

5.05v

-11.93v

T3 (High)

11.25A

12.00A

12.75A

1.87A

0.37A

309w / 263w

85.11%

26.5C / 45.8°C

19.3°C

3.33v

4.98v

11.94v

4.96v

-11.98v

T4 (Full)

15.00A

16.00A

17.00A

2.50A

0.50A

419w / 350w

83.53%

25.6°C / 44.7°C

19.1°C

3.31v

4.92v

11.96v

4.88v

-12.01v

T5 (x-load)

15.00A

16.00A

1.00A

0.00A

0.00A

175w /

138w

78.85%

27.2°C / 45.2°C

18.0°C

3.34v

4.75v

12.45v

5.16v

-12.50v

T6 (x-load)

1.00A

1.00A

29.50A

0.00A

0.00A

0w /

346w

00.00%

00.0°C / 00.0°C

0.0°C

0.00v

0.00v

0.00v

0.00v

-0.00v

T7 (MAX)

15.00A

16.00A

23.00A

2.50A

0.50A

507w / 420w

82.84%

27.3°C / 56.0°C

28.7°C

3.31v

4.93v

11.88v

4.86v

-12.06v

Starting with the results from Test 1-4 which best represent the PSU under normal usage, we can see that the +3.3v and +5v rails on the unit are reasonably stable with a drop of 0.06v and 0.17v respectively. The real shock however comes when we take a look at the results from the +12v rail which actually INCREASED by 0.04v from idle to full load. This normally occurs when the voltage regulation on the PSU overcompensates for the load and can actually end up reducing the total power output as a result. Efficiency, on the other hand is very good for such a small unit with 85% being achieved at a load of 180 - 260w.

Although it is quite unlike me to comment on the noise of a PSU given how loud the load testing equipment is, this is undoubtedly going to be an important factor in the decision of anyone purchasing a SFX PSU. Therefore, using my ear alone as the only measuring device, I can tell you that up to 200w load the SFX Power is very quiet. However as the load increases to 260w the 80mm fan speed increases significantly to the point where I imagine you'd easily be able to hear it across the room. At 350w I could actually hear the PSU above the load testing equipment, which is never a good sign!

T5 moves into the cross-load teritory and here we can see that the be quiet isn't so happy with a heavy load on the +3.3v and +5v rails and only a small load on the +12v rail. Voltages for the +5v rail hit a rather poor 4.75v and the +12v rail shoots up to 12.45v. Additionally efficiency during this test drops to around 78%. In T6 the cross-load is reversed with a minimal load being placed on the +3.3v and +5v rails and the rest on the +12v rail. Unfortunately during this test the be quiet unit refused to power on with anything above 25A on the +12v rail and therefore failed the test. What we do need to remember at this point though is that these cross-load results are highly unlikely to be reproduced by any PC system (especially a HTPC/SFF PC) in the real world. Only if you was intending to use the unit purely to power 12v devices and nothing else would this become an issue.

T7 sees the SFX Power hit a maximum output of 420w - 70w higher than that if its rated output. Given the size of the unit this is actually pretty respectable and shows that the unit has a little extra power to give should the need arise. At this load the voltages are still very respectable and efficiency is just shy of 83%.

be quiet! 350w SFX Scope Results @ Room Temperature

+3.3v

+5.0v

+12v

T1 (Low)

T2 (Med)

T3 (High)

T4 (Full)

T5 (x-load)

T6 (x-load)

T7

(MAX)

For those of you not familiar with the term 'ripple', this refers to the small fluctuations in voltage that occur in all PSU's on a milisecond scale. Large quantities of 'ripple' on a PSU can damage or kill components in your PC over time and therefore testing a PSU's performance in this area is just as important as any other part. Unfortunately ripple cannot be measured using a standard multimeter and requires a specialist device called an oscillioscope. The results you see above are taken from our Rigol 25Mhz 400MSa/s scope that can save 'screenshots' of its data to a USB memory stick.

A quick glance at the graphs above shows the most unruly rail to be the +3.3v one. However, even here the SFX Power manages to keep the ripple at just over 40mVpp in Test 4 and just under 40mVpp in Test 7. The +5v and +12v rails perform even better in comparison topping out at 21.6mVpp and 25.6mVpp respectively during Test 4. Only during the cross-load testing in T5 does the +5v rail break 50mVpp showing that the SFX Power isn't too keen on cross-load situations.

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Conclusion

Being the first SFX PSU reviewed on Overclock3D thus far, it does make it slightly difficult to draw a conclusion on its performance in relation to any alternatives on the market. However, as much as I told myself not to compare the be quiet! SFX Power to the likes of an ATX PSU, it has become increasingly obvious throughout the testing that the unit is easily capable of competing with some of its full-sized counterparts.

Take for example the efficiency. At anything between 200-300w load the unit managed a highly respectable 85%. This only dropped down to 83% at other load levels, and even when run well above specification at an impressive 420w in Test 7, still managed to keep its chin up at 82.84%. This will play an important part in keeping energy bills to a minimum, especially when HTPC's and SFF Home/NAS servers tend to be left on 24/7.

Moving on to the voltage stability there's very little to be concerned about here either. The +3.3v and +5v rails may not have been quite as stable as some of the 350W full-sized ATX PSU's I've tested in the past, but with voltages ending up at 3.31v and 4.92v at full load, you really cant complain. The +12v rail was a bit of an odd ball, starting at 11.92v and actually increasing to 11.96v as a larger load was applied. This would tend to indicate that the voltage regulation on the PSU is overcompensating for the load and potentially reducing the maximum power output of the PSU at the top-end. However, with the unit managing to hold a 420w load in the testing this certainly wont pose any problem to those looking to get a full 350w out of the unit.

The only area that the be quiet! SFX Power failed to deliver (which is a bit ironic given its name) was in the noise output. At anything up to around 75% load the unit was perfectly silent. However on pushing closer to the PSU's maximum output, the 80mm fan speed increased significantly bringing with it the annoying pitched squeal that only 80mm fans are capable of. By 100% load the fan could easily be heard above the din of the PSU testing equipment which leads me to believe you wouldn't want your HTPC / SFF PC to be in the same room as you when this PSU is running flat out.

The Good

- Efficient operation for such a small unit

- Reasonable voltage stability in the 'normal' tests T1-T4.

- Sleeved Cables and Black finish make it good looking for an SFX unit.

- Ripple was surprisingly good.

- 420w max output!

The Mediocre

- Didn't like the cross-load tests.

The Bad

- Noisy approaching full load.

Although the be quiet! SFX Power is far from perfect, being able to fit such a stable and efficient PSU into a Small Form Factor casing is worthy of award. For this reason the be quiet receives our recommended award.

Thanks to be quiet! for sending the SFX Power in for review. Discuss this review in our forums.